All-in-one smart sensors overcome physical limitations with embedded artificial intelligence algorithms to detect and analyze light, color, heat, etc, that cannot be physically measured. All spectroscopic analyses have been believed to rely on the dispersion of light and require bulky optical and heavy mechanical elements. However, miniaturized spectrometers without the need for light dispersion can be powered by combining a reconstruction algorithm with an electrically tunable transport-mediated spectral response based on van der Waals heterostructures with tunable band alignment and interlayer exciton dynamics (Figure A), representing our unique topic (its preceding research was published in Science). This enables us to analyze thousands of colors, identify material composition, and detect thermal radiation on a chip, not in a lab (Figure B).

Next-generation memory/system semiconductor devices are desired to break through the fundamental limitations of Moore's Law and maximize storage/process/communication functions. The emerging devices must improve performance, reduce footprint area, suppress power dissipation, minimize process cost, and diversify applications. We explore abrupt van der Waals contacts with ultra-low resistivity by exploiting the interface between the metallic surface states and the insulating bulk states of the topological insulators. On the other side, we implement anti-ambipolar phototransistors switchable by light wavelength (Figure A), fabricated by integrating a laterally confined quantum well with a vertically resonating plasmonic cavity (Figure B). This can build multi-valued logic gates that operate in a single device (Figure C), maximizing information density.

We investigate one-dimensional or zigzag superlattices formed in two-dimensional Dirac fermionic materials, allowing electrons to be treated like light (Figure A). Once electrons can be treated as light, focusing, collimation, diffraction, and interference featured in traditional optics can be implemented in electronic or quantum devices. Our goal is to control the transport or trajectory of ballistic charge carriers by using quantum point contacts, Veselago lens, Klein collimator, and local artificial atom substitution (Figure B) and to observe interference in the double slit or Aharonov-Bohm ring structures. Electron interferometers are known to require tuning magnetic fields typically, but we may be able to tune interference only with electric fields alone. Combining this idea with a Josephson junction may realize tunable and stable qubits.

We fabricate van der Waals heterostructures with a wide variety of two-dimensional quantum materials and engineer their interfaces to induce quantum phase transitions and exotic phenomena by introducing plasma exposure (Figure A) or laser illumination  (Figure B). Furthermore, we aim to implement superconducting quantum interference devices based on multiple Josephson junctions for electrically tunable and ultra-compact monolithic qubit platforms. Ultimately, we are planning to explore chiral Majorana states that can be induced in Josephson junctions through the combination of superconductors, topological insulators, ferromagnets, etc. This topic provides a great opportunity to participate in collaborative research with domestic and international research groups for those receiving support from large facilities.